This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to Japanese Application No. 11(1999)-287368 filed on Oct. 7, 1999, the entire content of which is incorporated herein by reference.
The present invention generally relates to a vehicle driving condition detection device. More particularly, the present invention pertains to a device for detecting lateral acceleration and sideslip angle of a vehicle.
Determining or measuring the vehicular sideslip angle is important from the standpoint of assessing a vehicle""s traveling direction. A ground vehicle speed sensor has been used to determine or measure the vehicular sideslip angle. However, the sensors can be relatively expensive and so efforts have been made to determine or measure the vehicular sideslip angle using a more inexpensive sensor.
Japanese Unexamined Patent Publication No. Hei. 8 (1996)-332934 discloses an idea for enhancing the estimating precision of the vehicle body sideslip angle by improving the road slant estimation precision. In this document, the calculation of the lateral slope of the road is as follows. On the basis of the vehicle model, the changing rate of the lateral speed of vehicle is estimated which is the product of the vehicle speed V and the slip angular velocity. A lateral acceleration deviation is calculated by subtracting the lateral acceleration Gy from the product of the vehicle speed V and the yaw rate "Ugr". The lateral acceleration deviation is added with the aforementioned estimated lateral speed changing rate and the low frequency component of the resulting sum is calculated as the quantity of the road slant.
However, in this system, the vehicle-body sideslip is derived from the road slant quantity which is calculated using the lateral speed changing rate or the slip angular velocity on the basis of the vehicle model, which results in that in addition to the lateral slope quantity modeling errors are included. Thus, even when the vehicle runs along a flat road, in addition to when the vehicle runs along a slanted or banked road such as a banked road, there is a concern with respect to a reduced precision in estimating vehicle body sideslip.
A need thus exists for a vehicle driving condition detection device which is capable of detecting vehicle driving condition quantities or variables such as sideslip angle with a relatively high accuracy irrespective of road surface conditions.
The vehicle driving condition detection device of the present invention includes a vehicle-body sideslip angle estimating device for estimating the vehicle-body sideslip angle on the basis of a vehicle motion model which depends on road surface slip conditions, a detecting device which detects whether or not the vehicle is running on a laterally sloping or banked road based on deviation between a detected slip angular velocity and a calculated slip angular velocity determined based on the estimated vehicle-body sideslip angle estimated by the vehicle-body sideslip angle estimating device, and a correction device for correcting a detected lateral acceleration when the detecting device detects that the vehicle is running on a banked or sloping road.
The vehicle-body sideslip angle estimating device is adapted to estimate the vehicle-body sideslip angle on the basis of the corrected lateral acceleration determined by the correction device. The detection device includes: a differentiating device in which the estimated vehicle-body sideslip angle determined by the vehicle-body sideslip angle estimating device is differentiated with respect to time; a slip angular velocity detecting device which detects a slip angular velocity on the basis of the detected lateral acceleration, a detected yaw rate, and a detected vehicle speed; a subtracting device which performs a subtraction between a slip angular velocity calculated at the differentiating device and the slip angular velocity detected at the slip angular velocity detecting device; and a comparing device which makes a comparison between the deviation calculated at the subtracting device and a threshold value.
The correction device is adapted to make a correction of the lateral acceleration in such a manner that a deviation between the detected lateral acceleration and a product of the detected yaw rate and the detected vehicle speed is subtracted from the detected lateral acceleration. The correction means is also adapted to correct the detected lateral acceleration on the basis of a gravity acceleration along a vehicle vertical direction.
In the present invention, detecting the slope or bank of the road and correcting the detected values such as lateral acceleration on the banked road are made separately. In detail, the detection of the banked or sloping road is made based on the deviation between the actually detected slip angular velocity and the calculated slip angular velocity derived from the vehicle-body sideslip angle on the basis of the vehicle mode. The slip angle based on the road surface condition depended on vehicle motion model does not include errors resulting from the road surface slip, but includes a constant value (DC component) error resulting from the sloped or banked nature of the road. Thus, the slip angular velocity as the change of the slip angle with the passage of time does not include such a DC error. On the other hand, the sensor detected slip angular velocity includes a DC error resulting from the slope or bank of the road. Thus, the deviation between both the slip angular velocities indicates DC error components as an indication of the sloping or banked nature of the road, which results in that irrespective of road surface condition, the sloped or banked road condition can be detected with very good or highly accurate precision. Upon detecting the laterally sloping or banked road, for example, the DC error component included in the detected lateral acceleration is calculated by obtaining the deviation between the detected lateral acceleration and the product of the detected yaw rate and detected vehicle speed. Subtracting the resulting DC error component from the detected lateral acceleration brings in the correction of the detected lateral acceleration. Though the deviation between the detected lateral acceleration and the product of the detected yaw rate and detected vehicle speed is the DC error component of the lateral acceleration which results from the slope of the road, an error component of the lateral acceleration may sometimes be found when the road surface is in a slip condition even though the road is a flat road. Thus, if a structure is employed wherein the lateral acceleration is always made to be corrected by calculating the lateral acceleration deviation, an erroneous correction would be made on the flat road. In the present invention, detecting the sloped or banked road is made with very high accuracy or precision, only when the slope of the road becomes obvious the detected lateral acceleration is brought into correction, which prevents erroneous correction. As a result, the detection of the lateral acceleration can be made with very high precision even when on a banked or sloping road in addition to when on a flat road.
To obtain the slip angular velocity from the slip angle which is estimated on the basis of the road surface condition dependent on the vehicle motion model, for example, it is possible to employ differentiation of the slip angle with respect to time in the differentiating device, which eliminates the DC error component in the estimated slip angle. In addition, the slip angular velocity can be calculated by substituting the sensor detected lateral acceleration, yaw rate, and vehicle speed into the related formula. Due to the fact that the deviation between both slip angles increases in proportion to the increase of the angle of road slope or bank, comparing the deviation with the predetermined threshold value makes it possible to recognize whether or not the road is a banked road or a road with a slope.
The lateral acceleration corrected in accordance with the present invention can be used, say, for estimating the sideslip angle, which makes it possible to estimate the sideslip angle on not only a flat road but a banked or sloping road as well. Although making an estimation of the sideslip angle by using lateral acceleration before it""s correction the resultant estimated value includes an error component, making an estimation of the sideslip angle by using lateral acceleration after it""s correction, the resultant estimated sideslip angle becomes free from the sloping or banked road and is very high in precision.